Anemia/thyroid issues

Idk if this would technically fit in this category, but it made the most sense. I’m 13 and I’m always abnormally tired (not normal teenager tired, it’s like I’m good, then I hit a brick wall) and I get a lot of headaches. My doctor is having me get tested for anemia, or thyroid issues. Some of my family members have similar things, but I was also told that I could’ve had mono, bc my friends brother was still contagious when I was hanging out with them. Idk what to expect, and what anemia, or thyroid issues actually are, so if you have any experiences, or information on it, please share